Cryptosporidious is an important enteric infection and a significant cause of diarrhea in humans. In patients with acquired immunodeficiency syndrome (AIDS), infection with this protozoan is a major cause of death, and in immunocompetent hosts it is a major cause of acute, self-limiting diarrhea. The pathophysiology of diarrhea in cryptosporidiosis has not been well studied. Severe malabsorption has been documented; however, in AIDS patients there also appears to be a significant secretory component. Our neonated pig model of cryptosporidiosis will allow us to critically study the mechanisms of this disease in the immunocompetent pig, and we propose to create a T helper cell specific immunodeficiency in these animals as a model for cryptosporidiosis in AIDS patients. We propose the hypothesis that the structural damage and ion secretion is a consequence of the activation of inflammatory cells in the lamina propria whose eicosanoid mediators induce ion secretion and that this response is persistent and amplified in the T helper suppressed host. In vivo perfusion studies of jejunum and ileum will determine alterations in mucosal permeability and quantify maldigestion/malabsorption components. In vitro studies will determine alterations in specific absorptive and secretory mechanisms, the cAMP and cGMP generating capacity, and patterns of eicosanoid synthesis which will be correlated with specific inflammatory cells in the lamina propria. Blocking agents of eicosanoid synthesis and receptor antagonists of inflammatory mediators will be examined for their ability to inhibit ion secretion, and conversely the major eicosanoids identified in infected tissue will be examined for their secretory activity. We will study cell free filtrates or lysates of cryptosporidia grown on lung fibroblast culture for enterotoxin- like activity in whole intestinal tissue, in human colonic epithelial cell cultures and in isolated porcine small intestinal epithelial cells. A critical comparison of these features in the normal and immune suppressed pig should yield definitive information on the diarrheal mechanisms and provide insite into the immune control of this infection.